It is known that an article having a microrelief structure that has a period of less than or equal to the wavelength of visible light on the surface, has an antireflection performance that is based on continuous change in the refractive index in the microrelief structure. Furthermore, it is also known that the microrelief structure exhibits super water-repellent performance as a result of a lotus effect.
Regarding the method for producing an article having a microrelief structure on the surface, for example, the methods described below have been suggested.
(i) A method of transferring a microrelief structure to a thermoplastic resin when a thermoplastic resin is injection molded or press molded, by using a stamper having a reverse structure of the microrelief structure on the surface.
(ii) A method of filling an active energy ray-curable resin composition between a transparent substrate and a stamper having a reverse structure of a microrelief structure on the surface, curing the resin composition by irradiation of active energy radiation, subsequently releasing the stamper, and thereby transferring the microrelief structure to the cured product. Alternatively, a method of filling an active energy ray-curable resin composition between the stamper described above and a transparent substrate, subsequently releasing the stamper to thereby transfer a microrelief structure to the active energy ray-curable resin composition, and then curing the active energy ray-curable resin composition by irradiation of active energy radiation.
Among these methods, attention has been paid to method (ii), from the viewpoint that the method exhibits satisfactory transferability of the microrelief structure and a high degree of freedom of the composition at the article surface, is capable of continuous production when the stamper has a belt shape or a roll shape, and exhibits excellent productivity.
Regarding the active energy ray-curable resin composition that is used for the method (ii), for example, the following compositions have been suggested.
(1) A photocurable resin composition containing an acrylate oligomer such as urethane acrylate, an acrylic resin having a radical polymerizable functional group, a mold releasing agent, and a photopolymerization initiator (Patent Document 1).
(2) A photocurable resin composition containing a (meth)acrylate such as ethoxylated bisphenol A di(meth)acrylate, a reactive diluent such as N-vinylpyrrolidone, a photopolymerization initiator, and a fluorine-based surfactant (Patent Document 2).
(3) An ultraviolet-curable resin composition containing a polyfunctional (meth)acrylate such as trimethylolpropane tri(meth)acrylate, a photopolymerization initiator, and a leveling agent such as a polyether-modified silicone oil (Patent Document 3).
Furthermore, Patent Document 4 suggests a solvent-free active energy ray-curable resin composition. However, a light transmissive article formed from this curable resin composition still has room for improvement in terms of scratch resistance. Furthermore, examples of a general technique for enhancing scratch resistance include a method of incorporating a silicone oil to a curable resin composition as a surface adjusting agent, and thereby imparting slip properties (for example, Patent Document 5), and a method of using a polyfunctional acrylate monomer (for example, Patent Document 6).
Furthermore, it has been disclosed that an article having a microrelief structure on the surface has at least two layers, including a transparent base, and a layer formed by a cured product of an active energy ray-curable resin composition, the layer being formed on the transparent base and has a microrelief structure transferred thereon (Patent Document 7). In addition, in order to impart adhesiveness between the transparent base and the layer formed by a cured product of an active energy ray-curable resin composition, and functionalities such as high hardness, investigations have been made on the addition of functional layers thereto (Patent Document 8).